Genome-Wide Transcriptional Response of Mycobacterium smegmatis MC2155 to G-Quadruplex Ligands BRACO-19 and TMPyP4

Combating multidrug-resistance in S. pneumoniae: a G-quadruplex binding inhibitor of efflux pump and its bio-orthogonal assembly

Antibiotic resistance poses a significant global health threat, necessitating innovative strategies to combat multidrug-resistant bacterial infections. Streptococcus pneumoniae, a pathogen responsible for various infections, harbors highly conserved DNA quadruplexes in genes linked to its pathogenesis. In this study, we introduce a novel approach to counter antibiotic resistance by stabilizing G-quadruplex structures within the open reading frames of key resistance-associated genes (pmrA, recD and hsdS). We synthesized An4, a bis-anthracene derivative, using Cu(I)-catalyzed azide-alkyne cycloaddition, which exhibited remarkable binding and stabilization of the G-quadruplex in the pmrA gene responsible for drug efflux. An4 effectively permeated multidrug-resistant S. pneumoniae strains, leading to a substantial 12.5-fold reduction in ciprofloxacin resistance. Furthermore, An4 downregulated pmrA gene expression, enhancing drug retention within bacterial cells. Remarkably, the pmrA G-quadruplex cloned into the pET28a(+) plasmid transformed into Escherichia coli BL21 cells can template Cu-free bio-orthogonal synthesis of An4 from its corresponding alkyne and azide fragments. This study presents a pioneering strategy to combat antibiotic resistance by genetically reducing drug efflux pump expression through G-quadruplex stabilization, offering promising avenues for addressing antibiotic resistance.

Selective targeting of parallel G-quadruplex structure using L-RNA aptamer

G-quadruplexes (G4) are special nucleic acid structures with diverse conformational polymorphisms. Selective targeting of G-quadruplex conformations and regulating their biological functions provide promising therapeutic intervention. Despite the large repertoire of G4-binding tools, only a limited number of them can specifically target a particular G4 conformation. Here, we introduce a novel method, G4-SELEX-Seq and report the development of the first L-RNA aptamer, L-Apt12-6, with high binding selectivity to parallel G4 over other nucleic acid structures. Using parallel dG4 c-kit 1 as an example, we demonstrate the strong binding affinity between L-Apt12-6 and c-kit 1 dG4 in vitro and in cells, and notably report the applications of L-Apt12-6 in controlling DNA replication and gene expression. Our results suggest that L-Apt12-6 is a valuable tool for targeting parallel G-quadruplex conformation and regulating G4-mediated biological processes. Furthermore, G4-SELEX-Seq can be used as a general platform for G4-targeting L-RNA aptamers selection and should be applicable to other nucleic acid structures.

Transcriptomic and metabolomic characterization of antibacterial activity of Melastoma dodecandrum

Antibacterial resistance poses a significant global threat, necessitating the discovery of new therapeutic agents. Plants are a valuable source of secondary metabolites with demonstrated anticancer and antibacterial properties. In this study, we reveal that Melastoma dodecandrum exhibits both bacteriostatic and bactericidal effects against Pseudomonas aeruginosa and Staphylococcus aureus. Treatment with plant extracts results in membrane damage and a reduction in P.aeruginosa swimming and swarming motility. A comparative analysis of bacterial transcriptomes exposed to M.dodecandrum extracts and four distinct antibiotics indicates that the extracts may trigger similar transcriptomic responses as triclosan, a fatty acid synthesis inhibitor. Activity-guided fractionation suggests that the antibacterial activity is not attributable to hydrolyzable tannins, but to unidentified minor compounds. Additionally, we identified 104 specialized metabolic pathways and demonstrated a high level of transcriptional coordination between these biosynthetic pathways and phytohormones, highlighting potential regulatory mechanisms of antibacterial metabolites in M.dodecandrum.

Revealing light-induced structural shifts in G-quadruplex-porphyrin complexes: a pulsed dipolar EPR study

The binding of G-quadruplex structures (G4s) with photosensitizers is of considerable importance in medicinal chemistry and drug discovery due to their promising potential in photodynamic therapy applications. G4s can experience structural changes as a result of ligand interactions and light exposure. Understanding these modifications is essential to uncover the fundamental biological roles of the complexes and optimize their therapeutic potential. The structural diversity of G4s makes it challenging to study their complexes with ligands, necessitating the use of various complementary methods to fully understand these interactions. In this study, we introduce, for the first time, the application of laser-induced dipolar EPR as a method to characterize G-quadruplex DNA complexes containing photosensitizers and to investigate light-induced structural modifications in these systems. To demonstrate the feasibility of this approach, we studied complexes of the human telomeric G-quadruplex (HTel-22) with cationic 5,10,15,20-tetrakis(1-methyl-4-pyridinio) porphyrin tetra(p-toluenesulfonate) (TMPyP4). In addition to showcasing a new methodology, we also aimed to provide insights into the mechanisms underlying photoinduced HTel-22/TMPyP4 structural changes, thereby aiding in the advancement of approaches targeting G4s in photodynamic therapy. EPR revealed G-quadruplex unfolding and dimer formation upon light exposure. Our findings demonstrate the potential of EPR spectroscopy for examining G4 complexes with photosensitizers and contribute to a better understanding of G4s' interactions with ligands under light.

Mechanisms of Phototoxic Effects of Cationic Porphyrins on Human Cells In Vitro

The toxic effects of four cationic porphyrins on various human cells were studied in vitro. It was found that, under dark conditions, porphyrins are almost nontoxic, while, under the action of light, the toxic effect was observed starting from nanomolar concentrations. At a concentration of 100 nM, porphyrins caused inhibition of metabolism in the MTT test in normal and cancer cells. Furthermore, low concentrations of porphyrins inhibited colony formation. The toxic effect was nonlinear; with increasing concentrations of various porphyrins, up to about 1 μM, the effect reached a plateau. In addition to the MTT test, this was repeated in experiments examining cell permeability to trypan blue, as well as survival after 24 h. The first visible manifestation of the toxic action of porphyrins is blebbing and swelling of cells. Against the background of this process, permeability to porphyrins and trypan blue appears. Subsequently, most cells (even mitotic cells) freeze in this swollen state for a long time (24 and even 48 h), remaining attached. Cellular morphology is mostly preserved. Thus, it is clear that the cells undergo mainly necrotic death. The hypothesis proposed is that the concentration dependence of membrane damage indicates a limited number of porphyrin targets on the membrane. These targets may be any ion channels, which should be considered in photodynamic therapy.

Transcriptional profiling of Mycobacterium smegmatis exposed to subinhibitory concentrations of G4-stabilizing ligands

The spread of Mycobacterium tuberculosis drug resistance accentuates the demand for anti-tuberculosis drugs with a fundamentally new mechanism of action without conferring cross-resistance. G-quadruplexes (G4, non-canonical DNA structures) are plausible new drug targets. Although G4-stabilizing ligands have been shown to inhibit mycobacterial growth, the exact mechanism of their action is uncertain. The aim of this study was to assess a possible correlation between putative G4 elements in a model mycobacterial strain M. smegmatis MC2155 and transcriptomic changes under the action of subinhibitory concentrations of G4 ligands BRACO-19 and TMPyP4. We also planned to compare the results with corresponding data previously obtained by us using higher, inhibitory concentrations of these ligands. For BRACO-19, we identified 589 (316↑; 273↓) and 865 (555↑; 310↓) differentially expressed genes at 5 µМ and 10 µМ, respectively. For TMPyP4, we observed the opposite trend, the number of differentially expressed genes decreased at higher concentration of the ligand: 754 (337↑; 417↓) and 702 (359↑; 343↓) for 2 µМ and 4 µМ, respectively. Statistical analysis revealed no correlation between ligand-induced transcriptomic changes and genomic localization of the putative quadruplex-forming sequences. At the same time, the data indicate certain functional specificity of the ligand-mediated transcriptomic effects, with TMPyP4 significantly affecting expression levels of transcription factors and arginine biosynthesis genes and BRACO-19 significantly affecting expression levels of iron metabolism and replication and reparation system genes.

[G-quadruplex structures in bacteria: functional properties and prospects for use as biotargets]

G-quadruplexes (G4), non-canonical secondary DNA structures, are intensively investigated for a long time. In eukaryotic organisms they play an important role in the regulation of gene expression and DNA repair. G4 have also been found in the genomes of numerous bacteria and archaea, but their functional role has not yet been fully explored. Nevertheless, their participation in the formation of antigenic variability, pathogenicity, antibiotic resistance and survival in extreme conditions has been established. Currently, many tools have been developed to detect potential G4 sequences and confirm their formation ability. Since the controlled formation and resolution of the quadruplex are significant means for the regulation of genes critical for survival, a promising direction is the search for ligands - compounds that can have a stabilizing effect on the quadruplex structure and thereby alter gene expression. Currently, a number of ligands are already known, their use stops the growth of pathogenic microorganisms. G4 ligands are of interest as potential antibiotics, which are extremely relevant due to the wide spread of drug resistant pathogens.